---
id: CVE-2026-88257
title: >-
  Improper Input Validation vulnerability in BeamMCP.Schema in ScriptKittyOS
  beam_mcp allows an MCP client to reach a tool's dispatch function with
  arguments that violate the input schema the server advertised
summary: >-
  Improper Input Validation vulnerability in BeamMCP.Schema in ScriptKittyOS
  beam_mcp allows an MCP client to reach a tool's dispatch function with
  arguments that violate the input schema the server advertised.
  BeamMCP.Schema.validate/2 ch…
severity: medium
cvss: 5.3
cvssVector: 'CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N'
cwe:
  - CWE-20
vendor: ScriptKittyOS
product: beam_mcp
affected:
  - beam_mcp >= 0.1.0 < 0.10.1
  - >-
    scriptkittyos/beam_mcp >= 083838eb8e17fe5f6fcaf761bdbe203110288b0b <
    289dbdbad641943b29a3b8d1eb36506cc8cec10a
published: '2026-10-08'
updated: '2026-10-08'
sourceUpdated: '2026-10-08T21:01:07.830'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-88257'
references:
  - url: 'https://cna.erlef.org/cves/CVE-2026-88257.html'
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: >-
      https://github.com/ScriptKittyOS/beam_mcp/commit/083838eb8e17fe5f6fcaf761bdbe203110288b0b
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: >-
      https://github.com/ScriptKittyOS/beam_mcp/commit/289dbdbad641943b29a3b8d1eb36506cc8cec10a
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: >-
      https://github.com/ScriptKittyOS/beam_mcp/security/advisories/GHSA-mrg2-4747-fmpw
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: 'https://osv.dev/vulnerability/EEF-CVE-2026-88257'
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
tags:
  - nvd
  - cve.org
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-10-08T13:59:14.866448Z'
cvssSource: cna
ingestedAt: '2026-10-08T14:47:16.344Z'
---

## Overview

Improper Input Validation vulnerability in BeamMCP.Schema in ScriptKittyOS beam_mcp allows an MCP client to reach a tool's dispatch function with arguments that violate the input schema the server advertised. BeamMCP.Schema.validate/2 checked type, required, additionalProperties, enum and numeric bounds on the top-level arguments object only. Constraints inside nested objects and on array items (items, minItems, maxItems, minLength, maxLength, pattern, nested required, enum and additionalProperties: false) were advertised by tools/list and never checked at tools/call or prompts/get, and keywords outside the enforced subset (oneOf, anyOf, $ref) were advertised and ignored.

A host whose dispatch code relies on the schema it declared receives values the schema forbids, such as an out-of-range number or an undeclared key inside a nested object. What the host does with such a value decides the impact.

This issue affects beam_mcp: from 0.1.0 before 0.10.1.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.